1. Field of the Invention
The present invention relates to a picture-reproducing apparatus and particularly, to the picture-reproducing apparatus which reproduces a moving picture from picture codes recorded on a record medium and has an automatic pause function.
2. Description of the Prior Art
Heretofore, technologies for effectively compressing a moving picture or a still picture in digital has been standardized. FIG. 12 shows a relationship between a sequence of decoding a moving picture from picture codes complying with MPEG-1 standard (ISO/IEC-11172) and a sequence of displaying the moving picture. In FIG. 1, I frame (intra picture) is decoded from only picture codes in the I frame itself. P frame (predictive picture) is reproduced from picture data in a preceding I frame if necessary and picture codes in the P frame itself. B frame (bidirectionally predictive picture) is reproduced from picture data in a preceding I frame or P frame if necessary, picture data in succeeding I frame or P frame if necessary, and picture codes in the B frame itself. P4 frame is reproduced from picture data in I1 frame if necessary and picture codes in P4 frame. B2 and B3 frames are reproduced from picture data in I1 frame if necessary, picture data in P4 frame if necessary, and picture codes in B2 and B3 frames, respectively. The display sequence has a order of I1, B2, B3, P4, and so forth. However, because frames B2 and B3 must be decoded using already decoded frame P4, frame P4 need to be decoded before frames B2 and B3. Therefore, the decode sequence must has a order of I1, P4, B2, B3, and so forth.
FIG. 13 is a diagram showing a relationship between a variation of the amount of picture codes in a buffer and frame types. According to the MPEG standard, compression method varies among frame types. Therefore, there is a tendency that an I frame which is decoded from picture codes in the I frame itself heavily consumes codes, whereas a B frame which is reproduced while using picture data of preceding I or P frame if necessary, picture data of a succeeding I or P frame if necessary lightly consumes picture codes. In order to simultaneously read picture codes from a recording media at a constant rate and execute a moving picture-decoding process in which the amount of consumed picture codes varies dependently on picture type, there is desired a picture code buffer which never overflows nor underflows. In addition, according to the MPEG standard, the amount of picture codes which should be stored in a picture code buffer at the time when the decoding of the first frame begins is described in xe2x80x9cvbv delay xe2x80x9d in a picture layer as shown in FIG. 10. Decoder needs to start decoding at the time when a picture code buffer has stored the amount of picture codes designated by xe2x80x9cvbv delayxe2x80x9d to prevent such phenomenon in which the picture code buffer underflows, the decoding operation of the decoder is halted, and the temporal continuity of the displayed picture breaks.
Among standards by which moving picture data are compressed in conformity with the MPEG standard or the CDROM-XA (Compact Disc Read Only Memory Extended Architecture) standard and then recorded on a compact disc having a sector structure is the Video CD standard. In the Video CD standard, there is provided an automatic pause function. In accordance with the automatic pause function, once a frame including a sector whose trigger bit for the automatic pause function (hereinafter referred to as xe2x80x9can automatic pause trigger bitxe2x80x9d) is active is decoded and displayed, the frame will be kept displayed in a freeze mode until the pause is released. In accordance with the structure of a sector defined by CDROM-XA Forum 2 as shown in FIG. 14, the automatic pause trigger bit is recorded in an automatic pause trigger bit area of Submode area of the sub header of a sector, and picture codes are grouped into sectors and recorded in a plurality of User Data areas.
As a prior art reference, JPA 07-226903 discloses an apparatus for realizing the automatic pause function.
FIG. 11 is a block diagram of the conventional picture-reproducing apparatus in the prior art reference. Referring to FIG. 11, the conventional picture-reproducing apparatus comprises: read-in circuit 32 which reads picture codes in User Data areas from recording media 31, which has a Submode area and User Data area in a structured sector, and writes the picture codes to buffer circuit 33; buffer circuit 33 which temporally stores the picture codes written by read-in circuit 32 and outputs the stored picture codes to decoder 34; decoder 34 which decodes picture data from the picture codes inputted from buffer circuit 33 and outputs the picture data to display circuit 35; and display circuit 35 which displays the picture data inputted from decoder 34.
The picture codes which are necessary to decode a single frame are recorded in the User data areas of a plurality of sectors dividedly. If there is a frame which is desired to be displayed in a freeze mode by automatic pause function, an active automatic pause trigger bit is recorded in a Submode of the last sector for the frame.
Next, the operation of read-in circuit 32 is explained hereunder with reference to FIG. 15.
At the beginning, read-in circuit 32 reads a Submode area at step S1501. Thereafter, read-in circuit 32 reads picture codes in a User Data area at step S1502 and writes the picture codes to buffer circuit 33 at step S1503. Thereafter, read-in circuit 32 judges whether or not all the picture codes in a User Data area of one sector has been read at step S1504. If the result of the judgement is negative, the operation returns to step S1502, whereas if the result of the judgement is affirmative, the operation advances to step S1505. Therefore, operations at Steps 1502 and 1503 are repeated until all the picture codes in a User data area of one sector has been read. Thereafter, read-in circuit 32 judges whether or not the automatic pause trigger bit in the Submode area read at step S1501 is active at step S1501. If the result of the judgement at step S1505 is negative, the operation returns to step S1501 to read the next sector, whereas if the result of the judgement at step S1505 is affirmative, the operation finishes and the next sector will not be read.
Next, the operation of buffer circuit 33 is explained hereunder with reference to FIG. 16.
As explained above, the picture codes are sequentially written to buffer circuit 33 by read-in circuit 32. Buffer circuit 33 judges whether or not decoding one frame is executable, that is, all the picture codes for one frame has stored in buffer circuit 33 at step S1601. If the result of the judgement at step S1601 is affirmative, the operation advances to step S1602, whereas if the result of the judgement at step S1601 is negative, the operation halts and buffer circuit 33 resumes the operation from step S1601 after a lapse of a predetermined time. After the operation has advanced to step S1602, buffer circuit 33 repeats to outputs the picture codes in one frame to decoder 34 until all the picture codes in the frame has outputted to decoder 34 at step S1602 and S1603. After exiting the loop of step S1602 and S1603, the operation returns to step S1601.
Next, the operation of decoder 34 is explained hereunder with reference to FIG. 17.
When picture codes are inputted from buffer circuit 33, decoder 34 decodes one frame from the picture codes at steps S1701 through S1703. In addition, if there is a decoded frame which is displayable in accordance with the display sequence, decoder 34 outputs the picture data of the decoded frame to display circuit 35.
Display circuit 35 displays picture data of decoded frames which have been inputted from decoder 34. If the input of picture data from decoder 34 is halted, display circuit 35 continues to display the picture data of the last frame before the halt in a freeze mode until the picture data of the next frame are inputted.
Next, the operation of the whole of the conventional picture-reproducing apparatus shown in FIG. 11 is explained hereunder with reference to FIGS. 18 and 19.
Referring to FIG. 18, there is illustrated an example in which frame B5 is displayed in a freeze mode by the automatic pause function. When read-in circuit 32 detects that the automatic pause trigger bit in the last sector of frame B5 is active, read-in circuit 32 will not read the next sector after writing the picture codes in the User Data area of the last sector of frame B5 to buffer 32. Because writing picture codes to buffer circuit 33 by read-in circuit 32 is halted, as shown in FIG. 19 in which an example of a variation of the amount of the picture codes in conventional buffer circuit 33 is illustrated, when the last decodable frame to which the picture codes stored in buffer circuit 33 belong becomes frame B5, buffer circuit 33 outputs the picture codes of frame B5 to decoder 34, and when this outputting operation completes, because picture codes necessary to decode one frame are exhausted, buffer circuit 33 halts outputting picture codes to decoder 34. When having finished to decode frame B5, decoder 34 transfers picture data of frame B5 to display circuit 35 because it is just a time when frame B5 is displayable in accordance with the display sequence as shown in FIG. 18. When having finished to decode frame B5, because the picture codes of the next frame or frame B6 will not be inputted for a certain period, decoder 34 halts decoding operation and therefore, transfer of the picture data of the next frame to display circuit 35 is halted. Display circuit 35 displays frame B5 when the picture data of frame B5 are transferred thereto, and thereafter continues to display frame B5 in a freeze mode because the picture data of the next frame following frame B5 will not be transferred for the certain period. The above operation realizes the automatic pause function. When the automatic pause is released, picture codes necessary to decode one frame are not stored in buffer circuit 33 as shown in FIG. 19. Therefore, it is necessary to prolong the period before resuming decoding process until the amount of picture codes necessary for stable decoding operation is reached in buffer circuit 33 by writing operation to buffer circuit 33 by read-in circuit 32. That is, it is necessary to prolong such period until at least the picture codes of frame B6 are accumulated in buffer circuit 33. In the example shown in FIG. 19, the decoding process resumes when the picture codes of frame B6 and succeeding frames are accumulated.
FIG. 20 shows an example in which the automatic pause trigger bit in the last sector of frame P7 is active. When read-in circuit 32 detects that the automatic pause trigger bit in the last sector of frame P7 is active, read-in circuit 32 will not read picture codes of the next sector after having finished to write the picture codes in User Data area of the last sector of frame P7 to buffer circuit 33. Because writing picture codes to buffer circuit 33 by read-in circuit 32 is halted, when the last decodable frame to which the picture codes stored in buffer circuit 33 belong becomes frame P7, buffer circuit 33 outputs the picture codes of frame P7 to decoder 34, and when this writing operation completes, because picture codes necessary to decode one frame are exhausted, buffer circuit 33 halts outputting picture codes to decoder 34. When having finished to decode frame P7, decoder 34 transfers picture data of frame P4 to display circuit 35 because it is just a time when frame P4 is displayable in accordance with the display sequence. When having finished to decode frame P7, because the picture codes of the next frame will not be inputted for a certain period, decoder 34 halts decoding operation. At this time, because decoding frames B5 and B6 is not executed due to the halt of the decoding process, it is not possible to transfer the picture data of frames B5 and B6 to display circuit 35. Therefore, frames B5 and B6 which must be displayed before frame P7 in the display sequence are not displayed. Thus, it is not possible to transfer the picture data of frame P7 to display circuit 35 although frame P7 has decoded. Therefore, display circuit 35 displays frame P4 when the picture data of frame P4 are transferred thereto, and thereafter continues to display frame P4 in a freeze mode because the picture data of the frames B5 and B6 are not transferred though frame P7 should be displayed in a freeze mode originally.
The conventional picture-reproducing apparatus has disadvantages as follows:
(1) For an I frame or P frame which succeeds B frame(s) in the display sequence, the decode order differs from the display order. When the automatic pause trigger bit of such I or P frame is active, read-in circuit 32 does not read the picture codes of the succeeding B frame(s) in the decode sequence. Therefore, B frame(s) which should be displayed before such I or P frame are not decoded. Therefore, there is a disadvantage that it is not possible to display a picture in a freeze mode at an I or P frame having a sector whose automatic pause trigger bit is active. Therefore, if it is needed to display a picture in a freeze mode at an accurate frame, there arise a restriction that such I or P frame must be excluded from the frames having a sector whose automatic pause trigger bit is active.
(2) Buffer circuit 33 manages whether picture codes of a decodable frame are stored therein in order to output picture codes to decoder in frame unit. Therefore, buffer circuit 33 must have a function to perform a control in frame unit in addition to a function of temporal storage. Thus there is a disadvantage that buffer circuit 33 becomes complicated.
(3) When the automatic pause function is executed and a picture is displayed in a freeze mode, buffer 3 is halted without storing a sufficient amount of picture codes to decode even one frame. Therefore, even read-in circuit 32 starts it""s operation to write picture codes to buffer circuit 33 just after release of the automatic pause, it is impossible to start decoding operation until a certain amount of picture codes necessary to perform decoding operation stable without underflow is reached in buffer circuit 33. Therefore, there is a disadvantage that it takes a time from releasing the automatic pause to displaying a picture of the next frame.
(4) Because the automatic pause function is triggered by a halt of writing operation of the picture codes of the next sectors to buffer circuit 33 by read-in circuit 32 and the halt is caused when read-in circuit 32 detects that an automatic pause trigger bit is active, there is a disadvantage that a sector whose automatic pause trigger bit is active must be located at the end of the frame to be displayed in a freeze mode or after such frame.
In order to overcome the aforementioned disadvantages, the present invention has been made and accordingly, has an object to provide a picture-reproducing apparatus which is capable of performing the automatic pause at any frame to which an active automatic pause trigger bit belongs.
The present invention has another object to provide a picture-reproducing apparatus which does not need a complicated buffer circuit.
The present invention has still another object to provide a picture-reproducing apparatus which has a short response time from release of the automatic pause to reproduction of the succeeding frames.
The present invention has further object to provide a picture-reproducing apparatus which is capable of performing the automatic pause function no matter which sector in a frame to be displayed in a freeze mode by the automatic pause function has an active automatic pause trigger bit.
According to a first aspect of the present invention, there is provided a picture-reproducing apparatus for reproducing a moving picture from picture codes recorded in a record medium having sectors, wherein picture codes and an automatic pause trigger bit are recorded in each of the sectors, the picture-reproducing apparatus comprising: a read-in circuit for reading the picture codes and the automatic pause trigger bit from each of the sectors in accordance with a decode sequence; code-inserting circuit for inserting a trigger detection code into the picture codes read by the read-in circuit if the automatic pause trigger bit read by the read-in circuit has an active value; a buffer for temporally storing the picture codes read by the read-in circuit; a decoder for reading the picture codes which have been temporally stored in the buffer, decoding picture data from the picture codes read from the buffer, and setting trigger information of each frame to an active value if the trigger detection code is inserted in the picture codes of respective frame or resetting the trigger information of each frame to an inactive value if the trigger detection code is not inserted in the picture codes of respective frame; a picture memory for temporally storing the picture data and the trigger information while making a relationship between the picture data and the trigger information with respect to a frame; a transfer control circuit for, in accordance with a display sequence, reading the picture data and the trigger information from the picture memory; and a display circuit for displaying a moving picture using the picture data read from the picture memory by the transfer control circuit; wherein when the transfer control circuit detects that the trigger information read from the picture memory has an active value, the transfer control circuit halts reading operation thereof from a succeeding frame, output a halt-requesting signal to the read-in circuit in order to cause the read-in circuit to halt operation thereof, and output the halt-requesting signal to the decoder in order to cause the decoder to halt operation thereof; and wherein when the transfer control circuit halts reading operation thereof, the display circuit displays a frame before the halt in a freeze mode.
According to a second aspect of the present invention, there is provided a picture-reproducing apparatus for reproducing a moving picture from picture codes recorded in a record medium having sectors, wherein picture codes and an automatic pause trigger bit are recorded in each of the sectors, the picture-reproducing apparatus comprising: a read-in circuit for reading the picture codes and the automatic pause trigger bit from each of the sectors in accordance with a decode sequence; code-inserting circuit for inserting a trigger detection code of an active value into the picture codes read by the read-in circuit if the automatic pause trigger bit read by the read-in circuit has an active value or inserting a trigger detection code of an inactive value into the picture codes read by the read-in circuit if the automatic pause trigger bit read by the read-in circuit has an inactive value; a buffer for temporally storing the picture codes read by the read-in circuit; a decoder for reading the picture codes which have been temporally stored in the buffer, decoding picture data from the picture codes read from the buffer, and setting trigger information of each frame to an active value if the trigger detection code of the active vale is inserted in the picture codes of respective frame or resetting the trigger information of each frame to an inactive value if the trigger detection code of the active value is not inserted in the picture codes of respective frame; a picture memory for temporally storing the picture data and the trigger information while making a relationship between the picture data and the trigger information with respect to a frame; a transfer control circuit for, in accordance with a display sequence, reading the picture data and the trigger information from the picture memory; and a display circuit for displaying a moving picture using the picture data read from the picture memory by the transfer control circuit; wherein when the transfer control circuit detects that the trigger information read from the picture memory has an active value, the transfer control circuit halts reading operation thereof from a succeeding frame, output a halt-requesting signal to the read-in circuit in order to cause the read-in circuit to halt operation thereof, and output the halt-requesting signal to the decoder in order to cause the decoder to halt operation thereof; and wherein when the transfer control circuit halts reading operation thereof, the display circuit displays a frame before the halt in a freeze mode.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of the best mode embodiments thereof, as illustrated in the accompanying drawings.